It's critical that you understand the poker rules for betting. In most games, you must 'ante' something – this is the amount to get in the round. It is typically a flat amount that you put in for every round. This money goes to the pot in the middle of the table. You will go around continuing to bet, adding money to the pot, or fold until you are down to two players. Then you will have the final showdown. At the end of the hand, the highest hand, that has not folded, wins the pot. Betting is usually done in clockwise order. When it's your turn to bet, here are your choices: 

Call 
When you call, you bet enough to match what has been bet since the last time you bet (for instance, if you bet a dollar last time and someone else bet a $1.25, you would owe twenty five cents). 

Raise 
When you raise, you match the last bet (you call) plus you raise the bet by a certain amount. Some games will have a limit to how much you can raise at once. Following the example above, if you had bet a dollar, the other person raised you a quarter, then you raise by another quarter. Thus, you owe the pot 50 cents. 

Fold 
When you fold, you drop out of the current hand. You do this because you believe you do not have a good possibility of winning. You do not have to add any more money, but you also do not have any chance of winning. The betting will continue until everyone has folded, called or raised the bet. When you are down to two players who have all called, you have your showdown.